On July 29, 2019, the Federal Circuit in Amgen Inc. et al. v. Coherus Biosciences Inc. unanimously affirmed the District of Delaware’s decision to dismiss Amgen’s complaint “[b]ecause prosecution history estoppel bars Amgen from succeeding on its infringement claim under the doctrine of equivalents.”C.A. 2018-1993, slip op. at 2 (Fed. Cir. July 29, 2019).

Amgen filed suit on May 10, 2017 against Coherus alleging infringement of U.S. Patent No. 8,273,707 (“the ’707 patent”), directed to methods of purifying proteins using hydrophobic interaction chromatography (“HIC”), based on Coherus’s abbreviated Biologic License Application (aBLA) for pegfilgrastim.Id. at 6.Among its allegations, Amgen alleged that Coherus infringed the ’707 patent under the doctrine of equivalents, as opposed to an allegation of literal infringement, “because the salt combination of used in Coherus’s process did not match any of the three expressly claimed salt combinations in the ’707 patent.”Id.Coherus’s manufacturing process contained several chromatography steps used to purify pegfilgrastim including a step involving a chromatography buffer containing a salt combination not recited in the claims of the ’707 patent.Id.

Coherus moved to dismiss the complaint under Fed. R. Civ. P. 12(b)(6) in view of Amgen’s prosecution of the application leading to the issuance of the ‘707 patent.Id.The magistrate judge issued a Report and Recommendation recommending that the motion be granted because Amgen surrendered salt combinations—aside from those claimed—during prosecution of the ’707 patent when it distinguished prior art.Id. at 6-7.The District Court adopted the magistrate’s Report and Recommendation and granted Coherus’s motion to dismiss.Id. at 7.

On appeal, the Federal Circuit noted its agreement with the District Court holding that “[p]rosecution history estoppel . . . bars Amgen from succeeding on its infringement claims under the doctrine of equivalents” because Amgen “clearly and unmistakably surrendered salt combinations other than the particular combinations recited in the claims.Id. at 8.Specifically, the Federal Circuit explained that argument-based estoppel applied to the facts at hand because Amgen distinguished prior art on the basis that it did not teach or suggest certain particular combinations of salts and even included a declaration in support thereof discussing those same particular combinations of salts.Id. at 9-10.

Amgen argued that it distinguished the prior art not on the basis of the particular salt combinations but on the basis that the prior art did not disclose increasing dynamic capacity and “any salt combinations at all.”Id. at 10.The Federal Circuit disagreed explaining that Amgen made multiple arguments in distinguishing the prior art; however, “our precedent instructs that estoppel can attach to each argument.”Id. at 10-11.The Federal Circuit continued:

Amgen did not rely on the combination of its asserted grounds to distinguish [the prior art], so prosecution history applies to the “particular combinations” ground regardless of the other two arguments made by Amgen.

Id. at 11.

Amgen further argued that the latest response during prosecution of the ’707 patent “must be the focus of any argument-based estoppel analysis” and the last response that Amgen submitted during prosecution of the ’707 patent did not contain the lack of salt combinations argument against the prior art.Id.The Federal Circuit disagreed explaining that “[t]here is no requirement that argument-based estoppel apply only to arguments made in the most recent submission before allowance.”Id.Nothing in Amgen’s last submission during prosecution of the ’707 patent disavowed the surrender of the unclaimed combinations of salts made in Amgen’s earlier submission.

Amgen reminds us that prosecution history estoppel applies to each and every argument made during prosecution of the patent-at-issue and regardless of when the argument was made.

When reviewing prosecution histories, we consider all arguments distinguishing prior art as issues to consider under the doctrine of equivalents. For our clients, we evaluate these issues to assess the scope of patent claims from the perspectives of both the patent owner and potential infringers.This analysis is also valuable to investors and licensees who can be more fully informed about the value of their investment or royalty payments.

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